The invention relates to a supporting mount, and specifically to methods and apparatus for supporting between a wafer table and a wafer stage used for semiconductor process.
Shock-absorbing mounts are widely used in a variety of applications. Above all, an optical apparatus used for semiconductor process requires high precision of imaging onto a target device. Springs have been used for damping of vibration transmitted from a wafer stage to a wafer table used for semiconductor manufacturing.
Current integrated circuit (IC) manufacturing practices use lithography photomasks (reticles) to apply various patterns to a photosensitized semiconductor wafer used to create the ICs. Reticles are typically high-precision plates that contain a pattern of extremely small images of the various components of an electronic circuit. A reticle is used as a master to transfer a plurality of the circuit pattern onto a photosensitized wafer. Current state-of-the-art lithographic system often must position an ultra-fine image to within 15 nanometers. Current circuit architectures often have conductor linewidths as narrow as 30 nanometers. Accordingly, lithography processing equipment requires advanced precision optical and mechanical systems and even higher precision systems will be required in the future, as still smaller images become common.
Lithographic exposure apparatuses are used to project images from the reticle onto the photosensitized wafer during semiconductor processing. A typical exposure apparatus includes a base frame having a lower enclosure that contains a wafer stage for holding a semiconductor wafer workpiece. The base frame also supports an optical device that holds a reticle stage and is arranged to project the images from a reticle carried by the reticle stage onto the wafer workpiece. The base frame typically supports the optical device through a vibration isolation system designed to damp and isolate vibrations between components of exposure apparatus so that vibrations in one component are not transmitted to the other.
This is deemed necessary because mechanical vibrations transmitted between components can adversely influence the accuracy of exposure apparatus. A potential problem with providing a spring between the wafer table and the wafer stage is that many if not most spring damper mechanisms provide high stiffness. In other words, the conventional damper mechanisms tend not to move flexibly (i.e., without stiffness) when the wafer stage is vibrated.
As such, it becomes increasingly necessary to devise a system that provides low stiffness between the wafer table and the wafer stage, thus avoiding transmission of vibration from the wafer stage to the wafer table.